Re: [PATCH 1/1] fix d_revalidate oopsen on NFS exports

[Chris Dunlop <chris@onthe.net.au>]

On Wed, Nov 30, 2011 at 08:22:39PM -0600, Dave Kleikamp wrote:
> On 11/30/2011 06:47 PM, Chris Dunlop wrote:
>>> It's also worth printing a message - this *is* a kernel bug of some description
>>> if it happens.
>> 
>> Like the below?  This covers the d_revalidate for 9p, afs, coda,
>> hfs, ncpfs, proc, sysfs.
>> 
>> Note:  jfs isn't susceptible to this problem, but the resolution
>> doesn't look like the other file systems, and from the comment
>> I'm not sure if the problem was really understood and if it's
>> doing the right thing:
> 
> This code, as well as the comments, were copied from vfat. It seems
> reasonable for case-insensitive but case-preserving behavior (not jfs's
> default). The safe thing is to drop the negative dentry if we don't know
> the operation.

In that case, it looks like the thing to do might be to add the
"protection" to the start of jfs_ci_revaliate(), per how the
original has been changed in vfat:

fs/fat/namei_vfat.c:
static int vfat_revalidate_ci(struct dentry *dentry, struct nameidata *nd)
{
        if (nd && nd->flags & LOOKUP_RCU)
                return -ECHILD;
        ...
}

E.g.:

----------------------------------------------------------------------
Don't oops when abused by broken layered file systems

Signed-off-by: Chris Dunlop <chris@onthe.net.au>
---
 fs/jfs/namei.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/jfs/namei.c b/fs/jfs/namei.c
index e17545e..5504f6e 100644
--- a/fs/jfs/namei.c
+++ b/fs/jfs/namei.c
@@ -1585,6 +1585,9 @@ out:
 
 static int jfs_ci_revalidate(struct dentry *dentry, struct nameidata *nd)
 {
+	if (nd && nd->flags & LOOKUP_RCU)
+		return -ECHILD;
+
 	/*
 	 * This is not negative dentry. Always valid.
 	 *
-- 
1.7.0.4

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